The genus Conus is equipped with a unique venomous mixture of conopeptides which secreted for predation and defense purposes. This work is aiming to explore and determine the effect of the crude venom of Conus flavidus, a wormhunting cone snail inhabiting the Red Sea, on the oxidant/ antioxidant system in mice using some oxidative stress biomarker assays. In addition to assess its histopathological effects on some treated organs. The LC50 were detected for the crude venom using the hemolytic assay (16.7 mg/ml) and male albino mice were injected intraperitoneally with ½ LC50 (8.3 mg/kg B.Wt). Biochemically, after 2, 4, 6, 12, 24 hours of injection the results revealed significant inhibition of superoxide dismutase (SOD) and catalase (CAT) activities in blood and liver in almost all time intervals comparing with control one. However, it showed elevation in lipid peroxide content (LPC), protein carbonyl content (PCC), nitric oxide level (NO) reduced glutathione content (GSH) and total antioxidant capacity (TAC) contents of both blood and liver in almost all time intervals. Histopathologicaly, liver and heart were dissected after 1, 3 and 7 days of injection. The treated liver showed vacuolar degeneration, karyolosis and pyknosis, mild blood sinusoidal congestion and centrilobular necrosis. The treated heart illustrated degenerated myofibrils,pyknosis, edema, blood vessel congestion, loss of striation normal construction and fascicular pattern in the myocardium. These results revealed that C. flavidus crude venom has distinct effects upon the oxidant/antioxidant cellular system and degenerative pathological effects in some tissues of treated animals, proving that this venom may contain bioactive peptides, which could be purified and used for further pharmacological and drug discovery investigations in the future